Process for making sodium chlorate



u 1950 J. c. SCHUMACHER 2,511,516

PROCESS FOR MAKING SODIUM CHLORATE Filed Oct. 51, 1945 Wash Woler z z 4Dlssolver C Refrigeration Cryslollizer Wash walefa D Molher LiquorCenlrlfuge D|l.NoG1O i Cry;fols

Discord Chlorole Dryer Sodium Chlorole Crys'lols INVENTOR JOSEPH 0.SOHUMACHER ATTORNEY NaC1O Mother Liguor Patented June 13, 1950 PROCESSFOR MAKING SODIUM CHLORATE Joseph C. Schumacher, Los Angeles, Calif.,as-

signor to Western Electrochemical Company, Los Angeles, Calif., acorporation of Nevada Application October 31, 1945, Serial No. 625,856

5 Claims, (01. 204-95) This invention relates to a process formanufacturing sodium chlorate.

One object of the invention is to provide an improved continuouselectrolytic process for making sodium chlorate. Other objects are toprovide for the continuous maintenance of the composition and conditionof the electrolyte for maximum energy eificiency and capacity inproducing sodium chlorate; to provide for a circulatin liquid of highchloride and high chlorate concentration through the electrolytic cell;and to provide for the production of sodium chlorate of high purity atan economical cost.

These and other objects are attained by my invention which will now bedescribed in detail, reference being made to the acompanying drawingdiagrammatically representing the steps and "flow of matrial in myprocess.

In general the process involves the electrolysis of an aqueous solutionof sodium chloride in an electrolytic cell having graphite anodes andsteel cathodes, the electrolyte being continuously circulated into andout of the electrolytic cells with continuous removal of excess sodiumchlorate and continuous replenishment of sodium chloride while theliquid is outside the cell. Referring to solution from the dissolver Ais pumped continu- :ously into an electrolytic cell B where it iselectrolyzed between graphite anodes and steel cathodes, the latterconveniently being the walls of the container and the steel pipe watercooling coils within the cell. The effluent from the electrolytic cell,now containing additional sodium chlorate formed in the electrolyticprocess as the liquid flows through the cell, is passed through arefrigerated continuous crystallizer C, where crystals of sodiumchlorate are precipitated, the

slurry being then passed into a centrifuge D,

which is conveniently of the continuous feed and from the solidcrystals. The centrifuged sodium chlorate crystals may be water washedif this is desired for greater purity in the product, the wash liquorbeing collected separately from the mother .liquor in order to avoidundue dilution of the lat- 6 in the electrolyte at the temperaturewithin the the electrolytic cell in accordance with the usual 5 1practice in making chlorate electrolytically. The

,discharge type, which separates the mother liquor tytic cell arewithdrawn from the system.

I have discovered that unusual efficiency and long continuous operationof the process above described can be attained by maintaining arelatively high concentration of both sodium chloride and sodiumchlorate in the electrolyte. Considering the sodium chloride constituentin the electrolyte, I have found that the concentration of this shouldbe maintained at not less than about grams to one liter of electrolyte,but may be greater than this concentration up to a nearly saturatedsolution, but should be enough below saturation to avoid the possibilityof precipitation of solid sodium chloride from the electrolyte at anylow temperature which may be encountered in the circulatory path of theelectrolyte in the process above described.

In my preferred. method of operation, the lowest temperature encounteredis in the sodium chlorate precipitation step where about 0 C. is apreferred operating temperature. Under this operating condition I havefound that a concentration of sodium chloride as high as grams per literdoes not precipitate sodium chloride even in the presence of thesaturation amount of sodium chlorate in the solution. Since thetemperature of cooling to precipitate excesssodium chlorate is notcritical at 0 C. but is selected to give the optimum operation in thisand other steps of the process,- it may vary as much as 10 C. in eitherdirection with corresponding changes in the permissible limit of sodiumchloride concentration in the infiuent electrolyte. Considering thesodium chlorate constituent in the electrolyte, I have found that theconcentration of this should be maintained at about 400 grams per literor more throughout the circulatory system. The upper limit ofconcentration of sodium chlorate is that concentration which at thetemperature of operation in the electrolytic cell will still remain insolution (not precipitate as solid) in the electrolytic cell; or, inother words, slightly less than a saturated solution of sodium chloratecell. Under the preferred operation conditions of my process, theelectrolytic cell temperature is maintained at about 45 C., and iscontinuously circulated through the cell, with the infiuent liquidhaving a chlorate content of about 460 grams sodium chlorate per liter,increasing in chlorate content on its flow between the electrodes andthrough the cell. The added chlorate in the efiluent liquor from theelectrolytic cell is precipitated in my process by coolin the eflluent,and separating out the sodium chlorate crystals, and then recirculatingthrough the electrolytic cell the warmed up mother liquid (saturated asto sodium chlorate at the said cooling temperature) after making it upto a high sodium chloride content. When the infiuent liquid to theelectrolytic cell is of about this concentration, the eliluent from theelectrolytic cell will, because of the electrochemical reactions,contain a higher concentration of sodium chlorate and a correspondinglylower concentration of sodium chloride, depending upon the amount ofoxidation of chloride to chlorate which has taken place in the passageof the electrolyte through the cell, and this in turn being dependentupon the time required for the electrolyte to pass through the cell unitand upon the energy input. As a typical example, using a narrow,elongated electrolytic cell such as that described in my copendingapplication, Ser. No. 625,858, in which the electrolyte passes throughthe cell at the rate of about 60 gallons per hour, the cell drawing 2500amperes per hour at 3.0 to 3.5 volts, with graphite anode currentdensity of 30 amperes per square foot and steel cathode density of about50 amperes per square foot, the eflluent liquor at about 45 C.temperature, contains about 560 grams per liter of sodium chlorate with92 grams per liter of sodium chloride. When this cell eilluent is cooledto about C. as in the crystallizer C of the diagram, about one-fourth ofthe sodium chlorate crystallizes out and may be separated from theliquid, as in a centrifuge, leaving a mother liquor containing about 160grams per liter of sodium chloride with about 425 grams per liter ofsodium chlorate. This mother liquor is then replenished with sodiumchloride to a concentration of about 175 grams per liter, as in thedissolver A in the diagram, and this liquid is again passed through theelectrolytic cell. In this illustrative example, the sodium dichromatewas maintained at about 3 to 4 grams per 7 liter of electrolyte, and thepH was maintained at about 6.1 by the required addition of hydrochloricacid solution to the influent cell liquid. Greater efficiency resultswhen concentrated sodium chlorate solutions are passed into the cell,and when a high current density at the anodes is used. Also the highchlorate content of the diluent from the cells permits crystallizing outthe excess sodium chlorate by cooling.

The continuous fiow of the electrolyte through the electrolytic cellprovides a means of controlling the temperature of the electrolyticreaction, too high a temperature resultin in a decrease in the life ofthe anodes, and in excessive gassing, and too low a temperatureresulting in a marked decrease in the rate of formation of the chlorate.The avoidance of local high temperatures gives maximum life to theanodes because their disintegration is slower, and of a uniform nature.The continuous flow of electrolyte through the electrolytic cell alsopermits the necessary close control of the pH value of the electrolytewhich has been found to be at an optimum in the range from 6.0 to 6.2,this being most important in getting efficient production of chlorate inthe electrolytic reaction, and at the same time suppressing thesecondary reactions, particularly those causing the evolution of gasessuch as oxygen, chlorine, and hydrogen.

Because of the continuous circulation of the electrolyte around theelectrodes in going through the cell from the entrance point to thedischarge point, substantially constant conditions of electrolysis aremaintained, and therefore optimum current density, electrolytecomposition, and temperature, may be employed, which is not possiblewith a stagnant electrolyte.

lhe use of the continuous circulation system for the electrolyte and theresultant uniform conditions in the system, also permits the use ofordinary mild steel vessels, pipe lines, etc., whereas much moreexpensive nickel or chrome nickel alloys would be required if the systemwere operated at a higher temperature or if a discontinuous process ofelectrolysis were used, or if the efiiuent required evaporativeconcentration in order to separate the constituents.

The circulation of a relatively high concentration of sodium chloratethrough the electrolytic cell has the great advantage that it permitsthe removal of the added sodium chlorate produced in that passagethrough the cell by the simple expedient of cooling the effluent so thatsodium chlorate crystallizes out and the maintenance of a high chlorideconcentration in the influent of the cell is necessary to provide theconstituents for the formation of the additional chlorate in the passagethrough the cell.

I claim:

1. In a process for making sodium chlorate by the electrolysis undernormal atmospheric pressures and at a temperature of about 45 C., of anaqueous solution containing sodium chloride and a small amount of sodiumchromate, the steps consisting of continuously withdrawing electrolytefrom an electrolytic cell, continuously passing into the saidelectrolytic cell an electrolyte consisting of the mother liquor fromsaid withdrawn electrolyte after cooling to remove the excess sodiumchlorate and containing not less than 75 grams per liter of sodiumchloride along with not less than about 400 grams of sodium chlorate perliter, said electrolyte having a pH value of about 6.1, andelectrolyzing the said circulating electrolyte between immersed carbonand iron electrodes under current density and voltage conditions adaptedto produce additional sodium chlorate.

2. In a process for making sodium chlorate by the electrolysis undernormal atmospheric pressures and at a temperature of about 45 C., of anaqueous solution containing sodium chloride and a small amount of sodiumchromate, the steps consisting of continuously withdrawing electrolytefrom an electrolytic cell, continuously passing into the saidelectrolytic cell an electrolyte consisting of the mother liquor fromsaid withdrawn electrolyte after cooling to remove the excess sodiumchlorate and containing a substantially saturating amount of sodiumchloride along with sodium chlorate in concentration not less than about400 grams per liter, said electrolyte having a pH value of about 6.1,and electrolyzing the said circulating electrolyte between immersedcarbon and iron electrodes under current density and voltage conditionsadapted to produce additional sodium chlorate.

3. In a process for making sodium chlorate by the electrolysis undernormal atmospheric pressures and at a temperature of about 45 C., of anaqueous solution containing sodium chloride and a small amount of sodiumchromate, the steps comprising continuously withdrawing electrolyte froman electrolytic cell, continuously passing into the said electrolyticcell an electrolyte consisting of the mother liquor from said withdrawnelectrolyte after cooling to remove the excess sodium chlorate andcontaining about 175 grams per liter of sodium chloride along withsodium chlorate in concentration not less than about 400 grams perliter, said electrolyte having a pH value of about 6.1, andelectrolyzing the said circulating electrolyte between immersed carbonand iron electrodes under current density and voltage conditions adaptedto produce additional sodium chlorate.

4. In a process for making sodium chlorate by the electrolysis undernormal atmospheric pressures and at a, temperature of about 45 C., of anaqueous solution containing sodium chloride and a small amount of sodiumchromate, the steps consisting of continuously withdrawing electrolytefrom an electrolytic cell, continuously passing into the saidelectrolytic cell an electrolyte consisting of the mother liquor fromsaid withdrawn electrolyte after cooling to remove the excess sodiumchlorate and containing a substantially saturating amount of sodiumchloride along with sodium chlorate in concentration not less than thatwhich would yield a solution saturated with respect to sodium chloratein the electrolyte if cooled to a temperature of about 0 C., saidelectrolyte having a pH value of about 6.1, electrolyzing the saidcirculating electrolyte between immersed carbon and iron electrodesunder current density and voltage conditions adapted to produceadditional sodium chlorate, precipitating out the additional sodiumchlorate by cooling the withdrawn effluent electrolyte, separating theprecipitated sodium chlorate from the mother liquor, restoring thesodium chloride content of said liquor to an approximately saturatedsolution, and continuously returning the restored mother liquor to theelectrolytic cell.

5. In a process for making sodium chlorate by the electrolysis undernormal atmospheric pressures and at a temperature of about 45 C., of anaqueous solution containing sodium chloride and a small amount of sodiumchromate, the steps consisting of continuously withdrawing electrolytefrom an electrolytic cell, continuously passing into the saidelectrolytic cell an electrolyte consisting of the mother liquor fromsaid withdrawn electrolyte after cooling to remove the excess sodiumchlorate and containing a substantially saturating amount of sodiumchloride along with sodium chlorate in concentration not less than about400 grams per liter, said infiuent electrolyte having a pH value ofabout 6.1, electrolyzing the said circulating electrolyte betweenimmersed carbon and iron electrodes to produce additional sodiumchlorate, cooling said efiiuent electrolyte to precipitate out saidadditional sodium chlorate, adding sodium chloride to restore theinfluent electrolyte to its original condition, and returning it to theelectrolytic cell.

JOSEPH C. SCHUMACHER.

REFERENCES CITED The following references are of record in the file 'ofthis patent:

UNITED STATES PATENTS Number Name Date 693,035 Lederlin Feb. 11, 1902727,813 Lederlin May 12, 1903 732,753 Lederlin July 7, 1903 802,205Gibbs Oct. 17, 1905 1,023,545 Bates et al. Apr. 16, 1912 1,143,586 LaibJune 15, 1915 2,180,668 Delavenna et al. Nov. 21, 1939 OTHER REFERENCESChemical and Metallurgical Engineering, No. 12, vol. 45, Dec. 1938,pages 692-696.

The Principles of Applied Electrochemistry, A. J. Allmand, 1912, pages340, 341.

Principles of Applied Electrochemistry, Allmand et al. 1924, pages388-391.

1. IN A PROCESS FOR MAKING SODIUM CHLORATE BY THE ELECTROLYSIS UNDER NORMAL ATMOSPHERIC PRESSURES AND AT A TEMPERATURE OF ABOUT 45*C., OF AN AQUEOUS SOLUTION CONTAINING SODIUM CHLORIDE AND A SMALL AMOUNT OF SODIUM CHROMATE, THE STEPS CONSISTING OF CONTINUOUSLY WITHDRAWING ELECTROLYTE FROM AN ELECTROLYTIC CELL, CONTINUOUSLY PASSING INTO THE SAID ELECTROLYTIC CELL AN ELECTROLYTE CONSISTING OF THE MOTHER LIQUOR FROM SAID WITHDRAWN ELECTROLYTE AFTER COOLING TO REMOVE THE EXCESS SODIUM CHLORATE AND CONTAINING NOT LESS THAN 75 GRAMS PER LITER OF SODIUM CHLORIDE ALONG WITH NOT LESS THAN ABOUT 400 GRAMS OF SODIUM CHLORATE PER LITER, SAID ELECTROLYTE HAVING A PH VALUE OF ABOUT 6.1, AND ELECTROLYZING THE SAID CIRCULATING ELECTROLYTE BETWEEN IMMERSED CARBON AND IRON ELECTRODES UNDER CURRENT DENSITY AND VOLTAGE CONDITIONS ADAPTED TO PRODUCE ADDITIONAL SODIUM CHLORATE. 